EFFECT OF MIXTURE COMPONENT CHARACTERISTICS ON PROPERTY AND PERFORMANCE OF SUPERPAVE MIXTURES

Transcription

1 EFFECT OF MIXTURE COMPONENT CHARACTERISTICS ON PROPERTY AND PERFORMANCE OF SUPERPAVE MIXTURES By SANGHYUN CHUN A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA

2 2012 Sanghyun Chun 2

3 To my beloved wife, Eunsong Lee and lovely son, Woobin Chun 3

4 ACKNOWLEDGMENTS It is a great pleasure for me to thank and acknowledge the individuals who advised and supported during the course of my doctoral program. First of all, I would like to express my heartfelt appreciation to my committee chairman, Dr. Reynaldo Roque for his invaluable guidance and support throughout my studies at the University of Florida. I would not have been able to reach this great moment of my life without his encouragement, advice, and mentoring. I would like to extend my gratitude to other committee members, Dr. Mang Tia, Dr. Dennis R. Hiltunen, Dr. Peter G. Ifju, and Dr. Claude Villiers, for their support to accomplish my doctoral study. I also would like to express my sincere appreciation to Mr. George Lopp, Dr. Jian Zou, Dr. Weitao Li, Michael Bekoe, and Cristian Cocconcelli for their constructive advice and assistance on laboratory testing, data analysis, and field works. Many thanks would also be given to all former and current students in the materials group of the Department of Civil and Coastal Engineering at the University of Florida for their help and friendship. Special thanks would go to Dr. Sungho Kim, Dr. Jaeseung Kim, Dr. Chulseung Koh, and Hyungsuk Lee for their encouragement and friendship. Lastly, I would like to thank my parents, Kijoon Chun and Wollim Myung, parentsin-law, Hwayoung Lee and Chunghee Shin, my sister, Seieun Chun, my brother, Sangkeun Chun, my wife, Eunsong Lee and my son Woobin Chun for their enduring trust, encouragement and support. 4

5 TABLE OF CONTENTS page ACKNOWLEDGMENTS... 4 LIST OF TABLES... 8 LIST OF FIGURES... 9 LIST OF ABBREVIATIONS ABSTRACT CHAPTERS 1 INTRODUCTION Background Hypothesis Objectives Scope Research Approach CHARACTERIZATION OF MIXTURE GRADATION AND RESULTING VOLUMETRIC PROPERTIES (DOMINANT AGGREGATE SIZE RANGE- INTERSTITIAL COMPONENT (DASR-IC) MODEL) Background Dominant Aggregate Size Range (DASR) DASR Porosity Interstitial Component (IC) of Mixture Gradation Disruption Factor (DF) Effective Film Thickness (EFT) Ratio between Coarse Portion and Fine Portion of Fine Aggregates (CFA/FFA) Summary IMPLEMENTATION OF BINDER AND MIXTURE TESTS ON FIELD CORES FOR SUPERPAVE MIXTURES IN FLORIDA Background Binder Recovery and Binder Tests Binder Recovery Penetration Test Viscosity Test Dynamic Shear Rheometer Test (DSR) Bending Beam Rheometer Test (BBR)

6 3.2.6 Multiple Stress Creep Recovery Test (MSCR) Mixture Tests Test Specimen Preparation Measuring, Cataloguing, and Inspecting Cutting Gage Points Attachment Test Procedure Resilient Modulus Test Creep Test Tensile Strength Test Superpave IDT Test Results Moisture-Damaged Projects Summary EVALUATION OF FIELD MIXTURE PERFORMANCE USING DASR-IC MODEL PARAMETERS Background Implementation of Gradation Analysis for Superpave Mixtures Evaluation of Gradation Analysis Results for Superpave Projects Evaluation of Field Mixture Performance Field Performance: Rutting Field Performance: Cracking Summary IDENTIFICATION OF PREDICTIVE MIXTURE PROPERTY RELATIONSHIPS AND MODEL DEVELOPMENT Background Existing Material Property Models in the HMA-FM-E Model AC Stiffness Aging Sub-Model Fracture Energy Limit Aging Sub-Model Key Elements for Material Property Relationships DASR-IC Model Parameters Initial Material Properties Factors Related to Non-Healable Permanent Damage Development of Predictive Material Property Relationships Relationships for Initial Material Properties Initial Fracture Energy Relationship Initial Creep Rate Relationship Models for Changes in Material Properties AC Stiffness Model Fracture Energy Limit Model Summary

7 6 EVALUATION OF DASR-IC CRITERIA USING HMA-FM-E MODEL Background Enhanced HMA Fracture Mechanics Based Model (HMA-FM-E Model) Input Module Model Prediction Results Relationships between DASR-IC Criteria and Model Prediction Results Summary CLOSURE Summary and Findings Conclusions Recommendations and Future Works APPENDIX: DETERMINISTIC PROCEDURE FOR ESTIMATION OF CRACK INITIATION TIME BASED ON CRACK RATING DATA LIST OF REFERENCES BIOGRAPHICAL SKETCH

8 LIST OF TABLES Table page 1-1 Mixture information of Superpave projects evaluated Asphalt binder used for Superpave projects evaluated Mixture information for 11 Superpave projects Project information for moisture-damaged sections Mixture information of Superpave projects analyzed DASR-IC parameters calculated for Superpave projects Crack initiation time and cracking status determined for Superpave projects Summary of input data characteristics for the HMA-FM-E model Data used for model prediction Predicted top-down cracking performance using HMA-FM-E model

9 LIST OF FIGURES Figure page 1-1 DASR and IC for three different types of mixture (After Kim et al., 2006) Overall research approach flowchart Mixture components for calculation of DASR porosity (Kim et al., 2006) Configuration of different DF values (Guarin, 2009) Effective film thickness vs. theoretical film thickness Conceptual drawing of film thickness effect Determination of CFA/FFA Penetration test results for Superpave projects Viscosity test results for Superpave projects Change in viscosity with aging for Superpave projects G * sinδ, 10 rad/sec at 25 C (77 F) for Superpave projects S(t), 60 seconds loading time at -12 C (10.4 F) for Superpave projects m-value, 60 seconds loading time at -12 C (10.4 F) for Superpave projects MSCR average recovery at 64 C (147.2 F) for Superpave projects MSCR nonrecoverable compliance at 64 C (147.2 F) for Superpave projects Measuring, cataloguing, and inspecting work for field cores Cut specimens for Superpave IDT tests Cutting machine used in this study Gage points attachment Superpave IDT tests Power model of creep compliance Determination of fracture energy and dissipated creep strain energy to failure Change in resilient modulus over time

10 3-17 Change in creep compliance over time Change in creep rate over time Change in tensile strength over time Change in failure strain over time Change in fracture energy over time Change in air voids over time Initial rate of reduction in normalized fracture energy over time Initial rate of reduction in normalized energy ratio over time Initial fracture energy and creep rate for Superpave projects evaluated Field rutting performance for Superpave projects evaluated Rutting performance evaluation using DASR-IC parameters Determination of observed crack initiation time for Project 1 and Field cracking performance for Superpave projects evaluated Cracking performance evaluation using DASR-IC parameters Schematic plot for AC stiffness at surface vs. age Schematic plot for creep rate vs. age Schematic plot for normalized change in AC stiffness vs. age Schematic plot for FE limit vs. age Two material property relationships FE limit aging curve at different initial FE (k 1 =3 (Roque et al. 2010)) Flowchart for development of predictive material property relationships Relationship between initial fracture energy and DASR porosity Relationship between initial fracture energy and disruption factor Relationship between initial fracture energy and effective film thickness Predicted vs. measured initial fracture energy

11 5-12 Relationship between initial creep rate and DASR porosity Relationship between initial creep rate and DF Relationship between initial creep rate and EFT Relationship between initial creep rate and CFA/FFA Effect of polymer modification on relationship between initial creep rate and CFA/FFA Relationship between initial creep rate and viscosity Relationship between initial creep rate and effective asphalt content Relationship between initial creep rate and G* sinδ Proposed AC stiffness model Proposed FE limit model General framework of the HMA-FM-E model Predicted crack amount increase over time using HMA-FM-E model Relationships between DASR-IC criteria and field cracking performance A-1 Determination of observed crack initiation time for Project 1 and A-2 Determination of observed crack initiation time for Project 3 and A-3 Determination of observed crack initiation time for Project 5 and A-4 Determination of observed crack initiation time for Project 7 and A-5 Determination of observed crack initiation time for Project 9 and A-6 Determination of observed crack initiation time for Project 11 and

12 LIST OF ABBREVIATIONS AASHTO AC APT ASTM BBR CFA/FFA DASR DF DSR EAC EFT ESAL FDOT FWD JMF HMA HMA-FM-E IA IC IDT ITLT IV MEPDG MSCR American Association of State Highway and Transportation Officials Asphalt Concrete Accelerated Pavement Testing American Society for Testing and Materials Bending Beam Rheometer Ratio of Coarse Fine Aggregate to Fine Fine Aggregate Dominant Aggregate Size Range Disruption Factor Dynamic Shear Rheometer Effective Asphalt Content Effective Film Thickness Equivalent Single Axle Load Florida Department of Transportation Falling Weight Deflectometer Job-Mix-Formula Hot-Mix Asphalt Enhanced Hot-Mix Asphalt Fracture Mechanics Based Model Independent Assurance Interstitial Component Indirect Tension Test Indirect Tension Test at Low Temperatures Interstitial Volume Mechanistic Empirical Pavement Design Guide Multiple Stress Creep Recovery 12

13 NCHRP PAV PG QA QC TCE TF UF VMA National Cooperative Highway Research Program Pressure Aging Vessel Performance Grade Quality Assurance Quality Control Trichloroethylene Theoretical Film Thickness University of Florida Voids in Mineral Aggregate 13

14 Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy EFFECT OF MIXTURE COMPONENT CHARACTERISTICS ON PROPERTY AND PERFORMANCE OF SUPERPAVE MIXTURES Chair: Reynaldo Roque Major: Civil Engineering By Sanghyun Chun August 2012 This study was conducted to evaluate the effect of mixture component characteristics (i.e. DASR and IC) on properties and performance of Superpave mixtures, specializing in the development of a set of implementable gradation and volumetric criteria, and Hot-Mix-Asphalt (HMA) mixture property predictive relationships based on mixture component characterization. Four DASR-IC model parameters including DASR porosity, DF, EFT, and CFA/FFA have formed the DASR-IC criteria to effectively address the two primary components (i.e. DASR and IC) of asphalt mixtures that play a major role on properties and performance. Field performance evaluation of different Superpave mixtures was conducted to identify the relationships between the four DASR-IC parameters and field performance. Based on results analyzed, it was found that the introduction of DASR-IC criteria as performance-related design parameters to current mix design guidelines and specifications will lead to better and more consistent field rutting and cracking performance of Superpave mixtures. In addition, the DASR-IC criteria will also provide a more rational method to consider the effect of DASR and IC on mixture behavior which strongly affects HMA 14

15 fracture properties. Therefore, it is expected that this criteria will have a potential to identify the effect of mixture gradation and volumetric characteristics on mixture fracture properties which is more reliably related to performance of asphalt mixtures. Relationships able to predict initial fracture energy and creep rate, which are the properties known to govern the change in material property over time and are also required for performance model predictions, were developed in this study. Furthermore, conceptual relationships were identified to describe changes in these properties over time (aging) by including the effect of the non-healable permanent damage related to load and moisture. This can serve as the foundation for further development of improved models to predict mixture properties as a function of age in the field based on additional field data and laboratory studies using more advanced laboratory conditioning procedures. The verified relationships will also serve to provide reliable inputs for prediction of service life using pavement performance prediction models. 15

16 CHAPTER 1 INTRODUCTION 1.1 Background It is now generally agreed that aggregate gradation is one of the most important factors that affects the properties and performance of asphalt mixtures. Having suitable gradation characteristics including appropriate aggregate particle size distribution and resulting volumetric properties is obviously important to ensure good field mixture performance. Therefore, aggregate related parameters have been studied to identify their effects on observed field performance of asphalt mixtures. Although different parameters, including effective film thickness and other volumetric parameters were found to affect mixture performance, consensus has not been reached regarding rational design guidelines and criteria, especially as related to the selection of the best aggregate blend to achieve optimal performance. The Superpave field monitoring project recently completed at the University of Florida has determined that existing mix design criteria included in Superpave system such as Voids in Mineral Aggregate (VMA), gradation control points, and effective asphalt content do not capture all critical aspects of gradation and resulting volumetric properties found to be most strongly related to field mixture performance (Roque et Al., 2011). Thereby, Superpave mixture performance varied significantly among mixtures that met all existing design and construction specification criteria. Therefore, there was a need to identify and verify additional criteria that can assure better and more consistent Superpave mixture performance. It was also found that differences in performance could not explained by differences in binder properties between mixtures. 16

17 It appeared that differences in performance were primarily controlled by differences in gradation and resulting volumetric properties between mixtures. According to previous work conducted by University of Florida researchers, gradation characteristics of mixture can be expressed by separating the gradation into two major components: Dominant Aggregate Size Range (DASR) and Interstitial Component (IC) (After Kim et al., 2006). It has been shown that parameters describing the characteristics of these components, which were determined based on packing theory and particle size distributions, seemed to be well correlated to mixture performance. Kim et al. (2006) indicated in their research that porosity can be used as a criterion to ensure contact between DASR particles within the asphalt mixture to provide adequate interlocking and resistance to deformation and fracture. The work has clearly shown that DASR porosity can be used as an indicator which reflects the characteristics of coarse aggregate structure. The schematic of the DASR and IC concept for three different types of mixtures is illustrated in Figure 1-1. DASR IC (a) SMA Mixture (b) Coarse Dense Mixture (c) Fine Dense Mixture Figure 1-1. DASR and IC for three different types of mixture (After Kim et al., 2006) The work has also concluded that properties and characteristics of IC will strongly influence rutting and cracking resistance of asphalt mixtures. For the purpose of IC 17

18 characterization, a new parameter called Disruption Factor (DF) was conceived and developed by Guarin (2009) to evaluate the potential of IC particles to disrupt the DASR structure. It was found that DF appeared to be one good indicator to describe IC characteristics with respect to volumetric distribution of IC. However, DF only considers volumetric distribution of IC to determine the potential of the finer portion of the mixture s gradation (i.e., IC) to disrupt the DASR structure. Therefore, there was a need to identify and develop additional parameters to more effectively characterize the IC of asphalt mixture with regard to stiffening effect of IC on mixture and structure of IC. 1.2 Hypothesis Since there was a need to address more aspects of IC characteristics to better capture the effects of IC on key mixture properties and expected performance, two new parameters, effective film thickness (EFT) and ratio of coarse fine aggregate to fine fine aggregate (CFA/FFA), were added in addition to DF in this study for further IC characterization. It was expected that these two parameters will provide a more rational way to identify mixture behavior as mastic which is considered to strongly affect Hot-Mix Asphalt (HMA) fracture properties. Therefore, the addition of EFT and CFA/FFA will give a more potential to identify the effect of IC characteristics on properties which is more reliably related to performance of asphalt mixtures. The following two hypotheses were made in this study. Interstitial component (IC) characteristics related to the aggregate structure and binder distribution within the IC have an important effect on mixture fracture properties as well as on pavement cracking performance. Gradation and volumetric parameters that effectively characterize the DASR and IC can be used to predict mixture fracture properties. 18

19 1.3 Objectives The primary objective of this study is to evaluate the effect of mixture component characteristics (i.e., DASR and IC) on properties and performance of Superpave mixtures. Detailed objectives are summarized as follows. Further develop the DASR-IC criteria to more effectively characterize both coarse (DASR) and fine (IC) portions of mixture gradation and resulting volumetric properties that play a major role on mixture performance. Evaluate and verify the DASR-IC criteria as an effective and implementable set of gradation and volumetric criteria for mixture design and construction specification that can help to assure better and more consistent field mixture performance. Identify key mixture component characteristics associated with mixture fracture properties and changes in these properties (i.e., fracture energy and creep rate) over time. Develop predictive relationships for mixture fracture properties, specifically fracture energy and creep rate, which have shown to strongly affect (or influence) pavement cracking performance in the field. Identify and further develop improved forms of the HMA fracture property aging model in an effort to more accurately predict pavement cracking performance. 1.4 Scope Eleven Superpave monitoring project field sections were evaluated including different types of gradation, aggregate, and asphalt binder. It is noted that fairly wide ranges of Superpave mixture were evaluated in this study. All mixture data were obtained or determined from field cores including gradation, binder properties, volumetric properties, and mixture properties. The standard University of Florida (UF) Superpave Indirect Tension Tests (IDT) were performed at 10 C and 20 C, to obtain the HMA fracture properties of the different Superpave mixtures used for evaluation. Enhanced Hot-Mix Asphalt Fracture Mechanics Based Model (HMA-FM-E) was 19

20 employed to evaluate criteria developed as a performance prediction model. Table 1-1 summarizes the mixture information of Superpave projects evaluated in this study. Table 1-1. Mixture information of Superpave projects evaluated Project Aggregate Binder Type Mixture Type (UF) ID Type Top Bottom Top Bottom 1 Granite PG PG C 19.0C 2 Granite PG PG C 19.0C 3 Limestone PG PG C 19.0C 4 Limestone PG PG C 19.0C 6 Limestone PG N/A 12.5F N/A 7 Limestone PG PG F 12.5F 8 Limestone PG PG C 12.5C 9 Granite ARB-5 PG FC F 10 Granite ARB-5 PG FC F 11 Granite PG PG C 12.5C 12 Granite ARB-5 PG FC F Note: Mixture Type: C = Coarse Mixtures, F = Fine Mixtures, N/A = Not Applicable 1.5 Research Approach This research is mainly focused on evaluating the effect of mixture component characteristics on properties and performance of Superpave mixtures in order to develop more implementable performance-related criteria and predictive mixture property relationships. The overall research approach to accomplish the objectives of this study is shown in Figure 1-2. Details for each phase of this research are described in the following sections. Development of DASR-IC criteria: (1) Identify key mixture component characteristics; (2) Identify and develop parameters to effectively characterize mixture component characteristics identified; (3) Evaluate relationships between parameters identified and field mixture performance; (4) Develop implementable performance-related criteria using parameters evaluated (i.e., DASR-IC criteria). Development of predictive mixture property relationships: (1) Identify key mixture properties to be evaluated; (2) Evaluate relationships between properties identified and mixture performance; (3) Evaluate relationships between parameters employed in DASR-IC criteria and mixture fracture properties; (4) Identify key elements associated with initial mixture properties and changes in these properties 20

21 over time (aging); (5) Develop predictive relationships for initial mixture properties; (6) Develop improved forms of mixture property aging model. Evaluation of criteria developed: (1) Evaluate criteria developed using performance prediction model (HMA-FM-E model); (2) Validate and refine criteria developed using additional field and laboratory data. Figure 1-2. Overall research approach flowchart 21

22 CHAPTER 2 CHARACTERIZATION OF MIXTURE GRADATION AND RESULTING VOLUMETRIC PROPERTIES (DOMINANT AGGREGATE SIZE RANGE-INTERSTITIAL COMPONENT (DASR-IC) MODEL) 2.1 Background Research recently conducted at the University of Florida has concluded that the gradation of mixtures can be characterized by separating the gradation into two major components: The Dominant Aggregate Size Range (DASR) and the Interstitial Components (IC) (Kim et al., 2006, Guarin, 2009, Roque et al., 2011). It was also shown that parameters describing the characteristics of two components, which were determined based on packing theory and particle size distributions, seemed to be well correlated to mixture performance. These parameters are DASR porosity, Disruption Factor (DF), Effective Film Thickness (EFT), and ratio of Coarse Fine Aggregate to Fine Fine Aggregate (CFA/FFA), which are used to address the following aspects of gradation characteristics: DASR porosity: coarse aggregate interlocking Disruption Factor (DF) : volumetric distribution of the IC Effective Film Thickness (EFT) : stiffening effect of IC on mixture CFA/FFA: structure of the IC Detailed descriptions with regard to the definition and calculation procedure of each parameter are included in the following sections. 2.2 Dominant Aggregate Size Range (DASR) The concept and theoretical development of DASR, which was defined as the interactive range of particle sizes that forms the dominant structural network of aggregate, was introduce by Kim et al. (2006). According to the DASR approach, there is an interactive range of particle sizes that primarily contributes to aggregate interlocking in asphalt mixtures. Particle sizes interacting with each other will form the 22

23 primary structure to resist deformation and fracture. Particle sizes smaller than the DASR will serve to fill the voids between DASR particles, called the interstitial volume. The IC particles combined with binder form a secondary structure to help resist deformation and fracture, and it is the primary source of adhesion and resistance to tension. Particle sizes larger than the DASR will simply float in the DASR matrix and will not play a major role in the aggregate structure. The DASR, which is determined by conducting particle interaction analysis based on packing theory, can be composed of one size or multiple sizes. It was concluded that the DASR should be composed of coarse enough particles, and that all contiguous particle sizes determined to be interactive can be considered as part of the DASR. 2.3 DASR Porosity Porosity has been widely used in the field of soil mechanics as a dimensionless parameter that indicates the relative ratio of voids to total volume. It has been determined that the porosity of granular materials should be no greater than 50 % for particles to have contact with each other (i.e. to be interactive) (Lambe and Whitman, 1969). Research conducted by Kim et al. (2006) indicated that porosity can be used as a criterion to ensure contact between DASR particles within the asphalt mixture to provide adequate interlocking and resistance to deformation and fracture. The basic principles related to the calculation of DASR porosity are as follows. The Voids in Mineral Aggregate (VMA) of asphalt mixtures, which indicates the volume of available space between aggregates in a compacted mixture, is comparable to volume of voids in soil. Porosity can be calculated for any DASR by assuming that a mixture has certain effective asphalt content and air voids (i.e. VMA) for a given gradation (Figure 2-1). Finally DASR porosity can be calculated using Equation

24 Figure 2-1. Mixture components for calculation of DASR porosity (Kim et al., 2006) DASR V V V ( DASR) T ( DASR) V V TM ICAGG V VMA AGG DASR (2-1) Where, η DASR = DASR porosity, V V(DASR) = volume of voids within DASR, V T(DASR) = total volume available for DASR particles, V ICAGG = volume of IC aggregates, VMA = voids in mineral aggregate, V TM = total volume of mixture, V AGG>DASR = volume of particles bigger than DASR. 2.4 Interstitial Component (IC) of Mixture Gradation As illustrated in Figure 1-1, the interstitial component is the material including asphalt, fine aggregates, and air voids that exists within the interstices of the DASR, and volume of this material is considered as the interstitial volume (IV). Research conducted by Guarin (2009) concluded that properties and characteristics of the IC will strongly influence the rutting and cracking resistance of asphalt mixtures. The IC should fill the voids within the aggregates larger than the IC without disrupting the DASR structure. As the DASR-IC model assumes that the particles bigger than the DASR are floating in the DASR structure, it would be reasonable to accept that 24

25 the effect of the DASR voids structure could be utilized to evaluate the total voids structure for the IC including the particles bigger than the DASR. Information on the IC characteristics is fundamental to understand and predict how the IC will fit into the IV and consequently to determine whether the DASR structure would be disrupted by the IC. The characteristics of the IC are expected to have a strong influence on key mixture properties including fracture energy and creep rate, as well as property changes due to aging. Therefore, it was expected that DASR-IC parameters would correlate well with the mixture performance, including rutting and cracking. 2.5 Disruption Factor (DF) A new parameter called the Disruption Factor (DF) was conceived and developed by Guarin (2009) to determine the potential of the finer portion of the mixture s gradation to disrupt the DASR structure. It was shown in laboratory studies that the DF can effectively evaluate the potential of IC particles to disrupt the DASR structure. DF can be calculated using the following equation. Volume of DF potentiall y distuptive IC particles Volume of DASR voids (2-2) Guarin also proffered an optimal DF range to attain better rutting and cracking performance of asphalt mixture. According to the DF approach, the IC aggregates would not be involved in transmitting load between the DASR aggregates if the DF is low. In this case, the DASR structure would get no additional support or benefit from the IC particles. In the case of high DF, mixture performance would be negatively affected because the DASR structure would be disrupted by the IC aggregates. Lastly, if the DF is in the optimal range, better mixture performance would be expected because the IC aggregates will be involved in resisting shear stresses with the DASR structure. 25

26 Therefore, it is expected that the DF will appear to be one good indicator to describe the IC characteristics with respect to the volumetric distribution of IC particles, and a link between the DF and material properties which are related to the performance of asphalt mixtures. Figure 2-2 is a pictorial representation of the different configurations of DF values: low, optimal, and high. (a) DF < Optimal DF range (b) DF = Optimal DF range (c) DF > Optimal DF range Figure 2-2. Configuration of different DF values (Guarin, 2009) 2.6 Effective Film Thickness (EFT) The film thickness of asphalt mixtures has been used to help explain aging phenomena, and many researchers have attempted to evaluate the relationship between film thickness and mixture performance. Kandhal and Chakraborty (1996) have shown that this parameter can be utilized as an indicator to characterize the durability and fatigue resistance of asphalt mixtures. However, it is still controversial with regard to its application in the mix design of HMA. More importantly, Superpave system does not have any requirements or guidelines regarding film thickness. Typically, apparent film thickness (or theoretical film thickness, TF), which is calculated by dividing the effective binder volume by the surface area of the aggregates, has been used for film thickness analysis. However, many researchers have questioned the relevance of this concept because it may not represent the distribution of binder in 26

27 the mixture. Nukunya et al. (2001) introduced a new concept of effective film thickness (EFT), which can be calculated by using the effective volumetric properties of asphalt mixture. They concluded that the effective volumetric properties including the EFT seem to effectively evaluate aging effects and correlated well with mixture properties. In this study, the EFT was selected to act as a surrogate to stiffening effect of interstitial component on mixture. Figure 2-3 is a pictorial representation of the difference between EFT and TF. The EFT can be calculated by using the following equation. V /100 be Pb Abs PAGG EFT ( microns) 1000 SAWT PFAGG SA PFAGG Gb (2-3) Where, V be = effective volume of asphalt binder, SA = surface area of fine aggregate, W T = total weight of mixture, PF AGG = percent fine aggregate by mass of total mixture, P b = asphalt content percent by mass of total mixture, Abs = absorption, P AGG = percent aggregate by mass of total mixture, G b = Specific gravity of asphalt binder. Mastic: Fine Aggregate + Asphalt Binder EFT (a) Effective Film Thickness Asphalt Binder: Uniformly distributed over all aggregate particles TF (b) Theoretical Film Thickness Figure 2-3. Effective film thickness vs. theoretical film thickness 27

28 Adequate interstitial volume is important for mixtures to have sufficient strain tolerance, which can be controlled by having an acceptable range of effective film thickness (EFT). EFT of asphalt mixtures is related to the stiffening effect of IC on mixture, and the fineness of the IC aggregates is the primary factor to control the EFT. In this study, the parameter EFT was evaluated and used to establish a set of performance-related design criteria and predictive relationships for fracture properties of asphalt mixtures. It was expected that the EFT is associated with the time-dependent response and brittleness of asphalt mixtures. For example, higher EFT results in higher creep rate and higher fracture energy. Figure 2-4 shows a schematic that conceptually illustrates how EFT affects mixture properties for two cases which have same component materials. σ 1 σ 1 σ 1 σ 1 σ 3 ε A = σ 1 /E AC ε B = (1/E AC )(σ 1 -νσ 3 ) σ 1 Case 1 σ 1 Case 2 Note: Then ε A > ε B, therefore, E A < E B Figure 2-4. Conceptual drawing of film thickness effect The white color portion of Figure 2-4 shows the asphalt binder part, while the gray color portion represents the aggregates. In the case of thicker EFT represented by case 1, material will tolerate higher strain (i.e. less brittle) than the thinner EFT (case 2) and it 28

29 % Passing will generally be broken by micro-damage development with high strain at low stress level. However, in the case of thinner EFT described by case 2, material will exhibit less strain tolerance and failed in a brittle manner with low strain at high stress (local stress) level. Therefore, mixtures should have an acceptable range of EFT for adequate strain tolerance and EFT can be controlled by limiting fineness of fine aggregate portion (i.e. IC) of mixture s gradation. 2.7 Ratio between Coarse Portion and Fine Portion of Fine Aggregates (CFA/FFA) Preliminary analyses indicated that the fineness of the fine aggregate portion of the interstitial components was strongly related to effective film thickness. However, EFT does not reflect the effect of particle interaction within the IC, which could be one important factor for IC characterization. Therefore, a new parameter CFA/FFA, which is the ratio between the coarse portion and fine portion of the IC particles, was introduced to characterize the structure of the IC of mixture s gradation FFA IC CFA DASR Low CFA/FFA - Too fine - High creep rate FFA IC CFA DASR #200 #16 #8 #4 (Sieve Size) High CFA/FFA - Too coarse - High creep rate Figure 2-5. Determination of CFA/FFA 29

30 In this study, CFA/FFA was used as an indicator to represent the fineness and aggregate structure of the IC. It was hypothesized that CFA/FFA was related to the creep response or time-dependent response of asphalt mixture. Figure 2-5 describes the basic principle of determining the CFA/FFA. 2.8 Summary For DASR-IC characterization, two existing parameters including DASR porosity and DF, and two more parameters including EFT and CFA/FFA were newly added, especially for further IC characterization. Finally, four parameters identified including DASR porosity, DF, EFT, and CFA/FFA have formed the DASR-IC criteria to effectively address the two primary components of asphalt mixtures (i.e. both coarse (DASR) and fine (IC) portions of mixture gradation and resulting volumetric properties) that play a major role on properties and performance. These parameters (i.e. four DASR-IC parameters) were used for evaluation conducted in this study. 30

31 CHAPTER 3 IMPLEMENTATION OF BINDER AND MIXTURE TESTS ON FIELD CORES FOR SUPERPAVE MIXTURES IN FLORIDA 3.1 Background Binder and mixture tests on field cores were conducted to determine binder and mixture properties for different Superpave projects in Florida. The information obtained was used to establish reasonable and effective mixture design guidelines and criteria, performance-related laboratory properties, and parameters, and predictive mixture property relationships. All binder tests were performed according to FDOT test methods, and HMA fracture mechanics model was used to analyze mixture test results. 3.2 Binder Recovery and Binder Tests Asphalt binder recoveries and binder tests were conducted for cores obtained from different Superpave projects. Binder tests, including penetration test at 25 C, viscosity test at 60 C, dynamic shear rheometer (DSR) test, bending beam rheometer (BBR) test, and multiple stress creep recovery (MSCR) test, were performed in this study. The binder testing plan is summarized below, and Table 3-1 represents the asphalt binder used on the Superpave projects evaluated. Penetration test at 25 C (77 F) Viscosity test at 60 C (140 F) Dynamic shear rheometer (DSR) test at 25 C (77 F) Bending beam rheometer (BBR) test at -12 C (10.4 F) Multiple stress creep recovery (MSCR) test at 64 C (147.2 F) Table 3-1. Asphalt binder used for Superpave projects evaluated Project Layer A Layer B PG PG PG PG PG PG Note: N/A = Not Applicable PG PG PG N/A PG PG PG PG ARB -5 PG ARB -5 PG PG PG ARB -5 PG

32 3.2.1 Binder Recovery Asphalt recovery was performed by using the solvent extraction method for cut cores obtained from the different Superpave projects, including Superpave top and bottom layers which were denoted as layer A and B, respectively. Trichloroethylene (TCE) was used as a solvent for binder recovery and the test procedure was carefully followed to minimize any additional aging of the binder during the binder recovery operation according to FDOT test methods Penetration Test The penetration test is one of the oldest and simplest empirical tests used to measure the consistency of asphalt binder. In general, penetration test is performed at 25 C which is considered approximately representative value of average service temperature for asphalt pavement. The depth of penetration is measured in units of 0.1 mm and reported in penetration units. For example, if the penetration depth of the needle is 8 mm, the penetration number of asphalt binder is 80. The description and practice of standard penetration test method is designated and reported in AASHTO T 49 and ASTM D 5. Penetration tests were conducted at 25 C. Figure 3-1 represents penetration test results from binder recovered for the Superpave projects evaluated. Results show that penetration measured for binder extracted from top layer denoted as layer A generally has lower value than for binder obtained from bottom layer denoted as layer B. This was expected because the effect of oxidative aging for top layer is generally more severe than bottom layer. Binders obtained from top layer of Project 9 and 10, which were rubber modified binder (ARB-5) exhibited especially lower penetration. 32

33 Penetration at 25 o C Penetration Test Results for Superpave Projects WP-Layer A WP-Layer B (U) 2(C) 3(C) 4(C) 6(C) 7(U) 8(C) 9(C) 10(C) 11(U) 12(C) Project (UF) ID Note: (C) = Cracked, (U) = Uncracked Figure 3-1. Penetration test results for Superpave projects Viscosity Test Viscosity represents the resistance to flow of a fluid and it can be simply defined as the ratio of shear stress to shear rate. As opposed to other empirical tests including penetration test, viscosity is a fundamental property. However, viscosity is generally measured at only one temperature, so it does not cover the full range of construction and service conditions. Viscosity test is usually performed at 60 C which is approximately considered to be representative of the maximum in-service surface temperature of asphalt pavement. The description and practice of standard absolute viscosity test method is described in AASHTO T 202 and ASTM D Figure 3-2 exhibits current viscosity measured from extracted binder and Figure 3-3 shows the change in viscosity over time for the Superpave projects evaluated. 33

34 Viscosity at 60 C (140 F), Poise Viscosity at 60 o C, Poises Viscosity Test Results for Superpave Projects WP-Layer A WP-Layer B (U) 2(C) (C) 3(C) 4(C) 6(C) 7(U) 8(C) 9(C) 10(C) 11(U) 12(C) Project (UF) ID Note: (C) = Cracked, (U) = Uncracked Figure 3-2. Viscosity test results for Superpave projects Change in Viscosity with Aging (Layer A) P1 P2 P3 P4 P6 P7 P8 P9 P Year Aged (a) Layer A P11 P12 34

35 Viscosity at 60 C (140 F), Poise Change in Viscosity with Aging (Layer B) P1 P2 P3 P4 P7 P Year Aged (b) Layer B Note: (C) = Cracked, (U) = Uncracked Figure 3-3. Change in viscosity with aging for Superpave projects P10 P11 P12 Due to more severe effect of oxidative aging caused by higher surface temperature, the top layer showed higher viscosity as well as higher rate of increase in viscosity than the bottom layer. Specifically, top layer (Layer A) of Project 8 through 12 which included polymer modified (PG 76-22) and rubber modified binder (ARB-5) sections indicated higher viscosity with around six to nine years of aging in the field. Also, as indicated in Figure 3-3 (a), these sections showed higher rate of increase in viscosity with aging Dynamic Shear Rheometer Test (DSR) The dynamic shear rheometer (DSR) test is used in the Superpave system to characterize the viscous and elastic behavior of asphalt binder at intermediate and high service temperatures. The DSR measures the complex shear modulus G * and phase angle δ of asphalt binder to determine the characteristics of elastic and viscous components at pavement service temperatures. Specifically, G * and δ measured are 35

36 G*Sinδ, kpa utilized as the indicators to predict two HMA distresses: rutting and fatigue cracking. The description and practice of standard DSR test method is designated and reported in AASHTO TP 5. In the Superpave asphalt binder specification, two parameters have been chosen (G * /sinδ, and G * sinδ) for evaluation of rutting and fatigue cracking, respectively. Since the Superpave projects investigated have six to eleven years of service period from the construction, all recovered binders obtained were considered as PAV aged binders. As the DSR test for PAV aged binder, samples were tested by using 8mm spindle at intermediate temperature determined based on the PG grade of original binder used. Figure 3-4 represents the parameter G * sinδ for all Superpave projects evaluated WP-Layer A WP-Layer B DSR G*Sinδ 10rad/s at 25 C (77 F) Superpave Maximum: 5000 kpa (U) 2(C) 3(C) 4(C) 6(C) 7(U) 8(C) 9(C) 10(C) 11(U) 12(C) Project (UF) ID Note: (C) = Cracked, (U) = Uncracked Figure 3-4. G * sinδ, 10 rad/sec at 25 C (77 F) for Superpave projects Figure 3-4 shows that all binders met the Superpave specification requirement for a maximum G * sinδ of 5000 kpa except for the top layer of Project 9 (ARB-5) and the 36

37 top and bottom layer of Project 10 (Top: ARB-5. Bottom: PG 64-22). G * sinδ is typically considered as an indicator of resistance to fatigue cracking because it indicates an amount of energy dissipated meaning that higher G * sinδ is related to higher energy loss. However, based on the results shown in Figure 3-4, and considering the cracking performance, it appeared questionable whether the parameter G * sinδ was consistently correlated with cracking performance of mixtures Bending Beam Rheometer Test (BBR) The bending beam rheometer (BBR) test is used in the Superpave system to determine the propensity of asphalt binders to thermal cracking at low temperatures. The BBR calculates the creep stiffness of asphalt binder (S(t)) and the rate of change of the stiffness (m-value). The creep stiffness (S(t)) is related to the thermal stresses developed in the HMA pavement as a result of thermal contraction, while the slope of the stiffness curve, m-value, is associated with the ability of HMA pavement to relieve thermal stresses. In other words, m-value is an indicator of the binder s ability to relax stresses by asphalt binder flow. The Superpave binder specification requires a maximum limit of creep stiffness and the minimum limit of m-value. The description and practice of standard BBR test method is designated and reported in AASHTO TP 1. The BBR tests for PAV aged binder samples were tested at PG grade temperature according to their original specification. Figures 3-5 and 3-6 represent the parameters S(t) and m-value as a result of the BBR testing for all Superpave project sections, respectively. Figure 3-5 shows that all binders met the Superpave specification requirement for a maximum S(t) of 300 MPa. Figure 3-6 indicates that all binders also met the Superpave specification requirement for a minimum m-value of 0.3 except for the top layers of Project 9 (ARB-5) and Project 10 (ARB-5). 37

38 m-value S(t), MPa WP-Layer A WP-Layer B BBR S(t), 60sec at -12 C (10.4 F) Superpave Maximum: 300 MPa (U) 2(C) 3(C) 4(C) 6(C) 7(U) 8(C) 9(C) 10(C) 11(U) 12(C) Project (UF) ID Note: (C) = Cracked, (U) = Uncracked Figure 3-5. S(t), 60 seconds loading time at -12 C (10.4 F) for Superpave projects BBR m-value, 60sec at -12 C (10.4 F) Superpave Minimum: WP-Layer A WP-Layer B (U) 2(C) 3(C) 4(C) 6(C) 7(U) 8(C) 9(C) 10(C) 11(U) 12(C) Project (UF) ID Note: (C) = Cracked, (U) = Uncracked Figure 3-6. m-value, 60 seconds loading time at -12 C (10.4 F) for Superpave projects The BBR test results including S(t) and m-value are typically evaluated to determine the propensity of binder for thermal cracking. However, based on the results 38

39 shown by Figure 3-5 and 3-6, it appeared also questionable whether the parameters S(t) and m-value were consistently correlated with cracking performance of mixtures Multiple Stress Creep Recovery Test (MSCR) The multiple stress creep recovery (MSCR) test is used to identify the presence of elastic response in the asphalt binder and the change of elastic response under shear creep and recovery using two different stress levels at a specified temperature. In general, the percent recovery of asphalt binders in the MSCR test is affected by the type and amount of polymer used in the polymer modified asphalt binder. Thus, it can be used as an indicator for determining whether polymer was utilized. In addition, nonrecoverable creep compliance has been used as an indicator of the asphalt binder s resistance to permanent deformation under repeated load. D Angelo et al. (2009, 2010) found that rutting is typically reduced by half as the non-recoverable creep compliance is reduced by half. The description and practice of standard MSCR test method is designated and reported in AASHTO TP and ASTM D The MSCR test was conducted by using an 8 mm spindle at the environmental grade temperature (64 C) for the State of Florida. Figure 3-7 and 3-8 represent the MSCR test results including average recovery and non-recoverable compliance for all Superpave project sections, respectively. Figure 3-7 clearly shows that MSCR average percent recovery can distinguish the presence of polymers in asphalt binders. In general, percent recovery of polymer modified binders was greater than base binders including PG and PG for both stress levels. Rubber modified binders also showed relatively high percent recovery than base binders. Since the percent recovery indicates the elastic response of asphalt binder, 39

40 Average Recovery (%) Average Recovery (%) polymer modified binders (PG 76-22) appear to exhibit higher elastic response and less sensitivity to change of stress level MSCR Average Recovery at 64.0 C (147.2 F) - Layer A P1 (PG 67-22) P2 (PG 64-22) P3 (PG 67-22) P4 (PG 67-22) P6 (PG 64-22) P7 (PG 64-22) P8 (PG 76-22) P9 (ARB-5) P10 (ARB-5) P11 (PG 76-22) kpa 3.2 kpa Project (UF) ID (a) Layer A P12 (ARB-5) MSCR Average Recovery at 64.0 C (147.2 F) - Layer B P1 (PG 67-22) P2 (PG 64-22) P3 (PG 67-22) P4 (PG 67-22) P7 (PG 64-22) P8 (PG 76-22) P9 (PG 64-22) P10 (PG 64-22) P11 (PG 64-22) kpa 3.2 kpa Project (UF) ID P12 (PG 64-22) (b) Layer B Figure 3-7. MSCR average recovery at 64 C (147.2 F) for Superpave projects 40

41 J nr (1/kPa) J nr (1/kPa) MSCR Non-Recoverable Compliance at 64.0 C (147.2 F) - Layer A P1 (PG 67-22) P2 (PG 64-22) P3 (PG 67-22) P4 (PG 67-22) P6 (PG 64-22) P7 (PG 64-22) kpa 3.2 kpa Project (UF) ID (a) Layer A P8 (PG 76-22) P9 (ARB-5) P10 (ARB-5) P11 (PG 76-22) P12 (ARB-5) MSCR Non-Recoverable Compliance at 64.0 C (147.2 F) - Layer B P1 (PG 67-22) P2 (PG 64-22) P3 (PG 67-22) P4 (PG 67-22) P7 (PG 64-22) P8 (PG 76-22) P9 (PG 64-22) P10 (PG 64-22) P11 (PG 64-22) kpa 3.2 kpa Project (UF) ID P12 (PG 64-22) (b) Layer B Figure 3-8. MSCR nonrecoverable compliance at 64 C (147.2 F) for Superpave projects Based on Figure 3-8, polymer and rubber modified binders normally showed lower non-recoverable compliance than base binders for both stress levels. According to 41

42 D Angelo et al. (2009), nonrecoverable compliance can be used for evaluating the rutting resistance of asphalt binder. However, on the basis of the results analyzed, it seemed questionable whether it is consistently correlated with rutting performance of mixtures in the field. 3.3 Mixture Tests Superpave IDT tests were performed on field cores obtained from the Superpave projects evaluated to determine mixture properties including modulus, creep compliance, strength, failure strain, and fracture energy and to identify the change in key mixture properties as a function of age in the field. Tests were performed at 10 C and 20 C Test Specimen Preparation Specimens were prepared for laboratory testing using field cores obtained from Superpave projects evaluated. Specific gravity (G mb ) test was conducted on each cut cores and air voids were calculated using the G mb and original (first time of coring) maximum specific gravity (G mm ). It should be noted that G mm could change with time, especially for moisture-damaged projects. For moisture-damaged projects, air voids determined using original G mm are probably conservatively low (i.e. true air voids of moisture-damaged projects are likely higher than air voids calculated using original G mm ). Cores of similar air voids were grouped for standard Superpave IDT tests Measuring, Cataloguing, and Inspecting Each core obtained was cleaned and the layer of each different asphalt mixture was properly identified, measured, and catalogued with appropriate markings to prevent any confusion. For quality control purposes, cores were inspected and compared to construction information to verify the presence of different mixtures and thicknesses. Figure 3-9 shows the measuring, cataloguing, and inspecting work for field cores. 42

43 Figure 3-9. Measuring, cataloguing, and inspecting work for field cores Cutting Once the data was properly logged and verified, the core was sliced to obtain test specimens for Superpave top and bottom layers for testing purposes. A cutting device, which has a diamond cutting saw and a special attachment to hold the cores, was used to slice the cores into specimens of desired thickness. Because the saw uses water to keep the blade wet, the cut specimens were placed in the dehumidifier for at least two days (i.e. 48 hours) to negate the moisture effects in testing. Figure 3-10 represents the cut specimens prepared for Superpave IDT tests and Figure 3-11 shows the cutting machine used in this study. Figure Cut specimens for Superpave IDT tests 43

44 Figure Cutting machine used in this study Gage Points Attachment Gage points were attached to the specimens using a steel template, a vacuum pump setup, and a strong adhesive. Four gage points (5/16 inch diameter by 1/8 inch thick) were placed with epoxy on each side of the specimens at distance of 19 mm (0.75 in.) from the center, along the vertical and horizontal axes. Figure 3-12 shows the gage point attachment procedure. Figure Gage points attachment 44

45 During this process, the loading axis previously marked on the specimens was checked and clarified. This procedure helped for the placement of specimen in the testing chamber and assured proper loading of the specimen Test Procedure One set of Superpave IDT tests including resilient modulus, creep compliance, and strength test were performed on each specimen for the Superpave projects evaluated to determine modulus, creep compliance, strength, failure strain, and fracture energy at 10 C and 20 C. These test results provide the properties to identify changes in key mixture properties over time with aging environment in the field. In addition, as it mentioned previously, this information was also critical to identify material properties and prediction model evaluation, and to calibrate and validate the pavement performance prediction model. The material testing system (MTS) used for this study, and test configuration of Superpave IDT test set-up are shown in Figure Figure Superpave IDT tests Resilient Modulus Test The resilient modulus is defined as the ratio of the applied stress to the recoverable strain when repeated loads are applied. The test was conducted according 45